[MNG-7879] Add a bom packaging

[gnodet]

JIRA issue: https://issues.apache.org/jira/browse/MNG-7879
Doc PR: apache/maven-site#451

The purpose of the BOM packaging is to more cleanly identify POM that will be consumed as BOM from POM that will be used as parents. The BOMs can be turned into a consumer POM, whereas parents can not lose any information.

[elharo]

This requires a correspnding update to https://maven.apache.org/guides/introduction/introduction-to-dependency-mechanism.html#bill-of-materials-bom-poms

I'm not sure how to manage that between 3.x/4.x and the two repos

[gnodet]

This requires a correspnding update to https://maven.apache.org/guides/introduction/introduction-to-dependency-mechanism.html#bill-of-materials-bom-poms

I'm not sure how to manage that between 3.x/4.x and the two repos

This is only a build time feature. The bom packaging is translated into a pom packaging at during the build/consumer transformation phase in order to keep full compatibility. This feature only targets Maven 4.x but will installed/deployed BOMs created with Maven 4 bom packaging will be consumed by Maven 3 with no problems.
The main goal of this feature has been explained in more details at #1160. The ability to differentiate between BOM that will be consumed and POM that will be used as parents is needed in order to translate the consumed poms to a compatible modelVersion 4.0.0.

We could definitely think about enhancing the consumer side so that this bom packaging would be installed / uploaded without the packaging translation, allowing the removal of the <scope>import</scope> weird thing. But that's out of scope for this specific PR.

[gnodet]

This requires a correspnding update to https://maven.apache.org/guides/introduction/introduction-to-dependency-mechanism.html#bill-of-materials-bom-poms

Doc PR: apache/maven-site#451

[cstamas]

How does this relate to #1247 ?

[gnodet]

How does this relate to #1247 ?

#1247 is based on this PR. There's no easy way to stack PRs on top of each other in Github. A few months ago, I had a single PR for all those changes, but I ended up splitting them in several smaller PRs. Some of them still depend on each other though.

[jira-importer]

Resolve #9033